1. Field of the Invention
The present invention relates to an image reading apparatus, a control method of an image reading apparatus, and a storage medium.
2. Description of the Related Art
Conventionally, there is an image reading apparatus that determines whether image data in a read document is color image data or monochrome image data. By performing such determination, the image reading apparatus can use, when performing image processing, parameters according to the type of image data. High image quality can thus be realized in the image to be processed.
Further, a conventional image reading apparatus conveys the document mounted on a document mounting unit and reads the image in the conveyed document. Among such image reading apparatuses, there is an image reading apparatus that reads the images on two sides of the document (i.e., a front side and a back side) in one conveyance process. It thus becomes unnecessary in such an image reading apparatus to read the document in two separate conveyance processes, i.e., the process for conveying the front side of the document and the process for conveying the back side of the document. As a result, time required for conveying the document can be reduced.
For example, Japanese Patent Application Laid-Open No. 2001-320557 discusses a configuration in which reading sensors for reading a two-sided document are disposed at a position facing the front side and a position facing the back side respectively. Both sides of the document can thus be read in one conveyance process.
However, the image reading apparatus which reads the document while conveying the document reads, when reading the front side of the document, an image on the front side of the document after causing the document to pass through a curved document conveyance path. The image reading apparatus may thus be unable to correctly determine the document due to vibration generated when conveying the document.
Such a problem will be described in detail below with reference to an image reading apparatus illustrated in FIGS. 11A and 11B. Referring to FIGS. 11A and 11B, the image reading apparatus conveys a document 102, using conveyance rollers 109, 110, 111, and 112, and reads the document 102 using a reading unit 114.
FIG. 11A illustrates a state in which a leading end portion of the document 102 that is conveyed by being greatly bent, has reached a reading position of the reading unit 114. In such a state, the conveyance roller 112 is not involved in the conveyance process, so that conveyance control of the document 102 is performed by only the conveyance rollers 109, 110, and 111.
Further, FIG. 11B also illustrates a state where a trailing end portion of the document 102 is to be read by the document 102 being greatly bent. Since the conveyance roller 109 becomes uninvolved in performing conveyance control in such a state, the conveyance process is performed by only the conveyance rollers 110, 111, and 112.
When the image reading apparatus reads the leading end and the trailing end portions of the document 102 as described above, shift and distortion that are difficult to estimate are generated in performing conveyance control. This is different from when the image reading apparatus conveys other regions of the document 102.
As a result, the read image data acquired in the above-described states may not become correctly read values for each pixel.
In particular, when a charge-coupled device (CCD) is employed as a reading device, a reading line position for each color component is different. The reading value of each component for the pixel may thus not be correctly acquired even when values between the lines of the sensor corresponding to the color components are corrected.
As described above, when one reading sensor reads one side of the document, color information of a predetermined region included in a front side of the document may not be correctly read. This is due to the positions in which the reading sensors are disposed and the curved shape of the document conveyance path. The predetermined region is, for example, the leading end and the trailing end portions of the document with respect to a conveying direction thereof.
To solve such a problem, the predetermined region positioned at the leading end portion of the document to be read by the front side reading unit may not be set as a region for determining the color. In such a case, if a color pixel is included in the predetermined region, the document may not be correctly determined as a color document. For example, such a case may occur when the region other than the predetermined region in the document is a monochrome image.